It is known that toothbrushes of the most varied shapes and constructions are common on the market. Toothbrushes displaying a metal portion within the handle have also been on offer, especially in the past. An example is disclosed in GB 2050156.
The need has recently arisen to manufacture a toothbrush consisting mainly of plastic material (essentially polypropylene and elastomere), for it to appeal in terms of handling and to be resistant to external agents (water, toothpaste, and so on), but also being provided with a particularly sturdy inner core, such as a metal core.
A metal-core toothbrush has some significant advantages over conventional, full-plastic toothbrushes. Firstly, the metal material (or equivalent), having a much larger elastic modulus than plastic materials, allows to achieve greater strength, longer duration and innovative elastic properties. Moreover, due to the increased strength of the material, it is possible to largely reduce the dimensions—in particular the resistant section—of the structural part of the toothbrush, for example of the neck portion between the handle and the bristle head. That makes the toothbrush ergonomically more advantageous, because it stands apart for its slimness precisely in the portion which interferes with the user's mouth and where it is hence most appreciated when the bulk is minimal. Increased ergonomics also translate into better manoeuvrability and, in the last analysis, in increased cleaning effectiveness.
The plastic component, in addition to pleasant tactile sensations, ensures good protection of the metal component from any oxidation or contact with the mouth lining (which contact might underlie allergic reactions).
Furthermore, the combination of the metal component with the plastic component, provided the latter is sufficiently clear, allows to obtain innovative and valuable aesthetic effects.
Finally, the presence of a core of a material with a high specific weight allows to achieve innovative results in terms of the weight and balancing of the toothbrush.
Beyond these immediately understandable aspects, the known art does not offer yet an effective process to be able to assemble a plastic toothbrush with a metal core. As a matter of fact, technological difficulties exist in combining these two so incompatible materials, both in terms of their nature, and in terms of processing.
In particular, it is necessary to identify a configuration and a process suitable for maintaining the inner core securely fastened in the mould and suitably exposed to be able to embed it and join it correctly to the plastic material injected into the mould.
Moreover, it would also be desirable to be able to have a process available which allows to introduce the use of a core into a toothbrush moulding method which, by becoming consolidated, has already allowed to achieve excellent results in terms of quality, economy and yield.
Moreover, in the toothbrush moulding process, the need arises to tuft the head portion by resorting to in-moulding or anchor-less processes, for the entire manufacturing process to remain effective and for it to be able to exploit uniform equipment.
However, it has been detected that these techniques still have drawbacks ensuing from the moulding of plastic material in the proximity of an enlarged portion of tuft root.
As a matter of fact, once the tufts have been processed to obtain an enlarged end or head, there are essentially two ways to anchor them to the remaining toothbrush portion. A first way provides to introduce the tufts into a suitable mould mask and hence to inject the remaining toothbrush head portion, wherein the enlarged ends remain embedded and joined together. In this case it is possible to suitably configure the mould and the mask to reduce to a minimum the problems during plastic injection.
A second way provides to introduce and fasten the tufts on a plate intended to then be fastened to the remaining toothbrush portion, which it will permanently form a part of.
In this last case, evidently, the plate is a toothbrush component which hence, both in terms of material and of the configuration, cannot be best adapted based solely on moulding requirements. It may therefore happen that, should it be required to inject molten plastic under pressure in the proximity of such component, leaks of material occur between the individual tufts and the respective housing holes.
This happens because the individual tufts are inserted in the holes and, despite being molten at their ends to form enlarged ends, they maintain a certain axial sliding play. The plastic material injected in the proximity of the enlarged end hence tends to seep in between such head and the plate, and then to leak out in the gap G (see FIG. 6A) between filaments F and the perimeter H of the holes, which is certainly not sealed due to the very structure of the tufts.
The seepage of plastic material, as may be guessed, causes unpleasant burrs and the possible disassembly of the topography of the tufts on the toothbrush.
Examples of injection techniques are disclosed in EP 567 672, which, however, remain not fully satisfactory.
The object of the present invention is hence that of providing an innovative manufacturing process of a toothbrush as described above, which allows to combine the advantages of the consolidated moulding processes of plastic toothbrushes with the advantageous introduction of a core, in particular a metal core.
A further object of the invention is that of providing a system which allows to perform an injection of plastic material at the desired pressure, even in the proximity of the bristle head, without substantial limitations and without leakages of material occurring between the tufts and the respective holes.